I shoulda read the instructions better, but instead, I delved into my whole music library, cleaning up all the tags in all kinds of ways. Then I couldn't figure out how to rewrite the whole mess back to my library. It seems one can clean up a tag, like genre, then select all the songs in one genre and save them without changing anything else. Then move on to the next genre, and the next ... But I can't find a way to just write the whole mess back at one time.